Effect Of Surfactant Chain Length Research Articles

Effect of Surfactant Chain Length on Emulsification Dynamics of Self Emulsifying Formulation of Poorly Soluble Drug.

In this work, the aim was to study the effect of the chain length of surfactant on the self emulsifying system of a poorly soluble drug, aceclofenac. The selection of almond oil as a lipid vehicle was done on the basis of solubility and compatibility of the vehicle with the drug. The effect of varying chain length of different surfactants of Tween series, namely Tween 20, Tween 40, Tween 60 and Tween 80, was evaluated on self emulsifying efficiency by constructing the pseudoternary diagrams. PEG-400 was used as a co-surfactant in a definite ratio with all the surfactants to minimize their concentration. The best self emulsifying ability was exhibited by Tween 80: PEG-400 combination followed by Tween 60: PEG-400, Tween 40: PEG-400, Tween 20: PEG-400. This observation indicates that as the chain length of Tweens increases, their ability to form a good microemulsion increases if the same co-surfactant is used. However, it has also been found that the presence of unsaturated bond in Tween 80 provides it an elasticity which supports good intermixing of oil and water, leading to formation of a fine microemulsion. Six different formulations were prepared using a combination of almond oil, Tween 80, PEG-400 and the drug aceclofenac. The formulations were subjected to various evaluation parameters, such as dispersibility, transmittance, pH, globule size, polydispersibility, zeta potential, viscosity, refractive index and in vitro dissolution. The best formulation was found to have globule size of less than 100 nm and zeta potential of -3.35 ± 0.60 mV, indicating the formation of a microemulsion of aceclofenac with good stability.

Unraveling the effect of surfactant chain length on the binding interaction of curcumin with cationic and non‐ionic micelles

AbstractMajor drawbacks of using curcumin as a potential multifunctional drug are its very low water solubility and lack of bio‐availability. For this purpose we have used surfactants to increase the solubility of curcumin in aqueous medium and to assess its hydrophilic and hydrophobic interactions with micelles. In order to understand the molecular mechanism of the interaction of curcumin with surfactants, we have employed cationic and non‐ionic surfactants. We have used hexadecyl(cetyl)trimethylammonium bromide (CTAB), tetradecyltrimethylammonium (TTAB) and dodecyltrimethylammonium bromide (DTAB) as cationic surfactants of varying hydrocarbon tail dimension and octylphenol ethoxylate with 10 moles of ethyelene oxide (OPE‐10), octylphenol ethoxylate with 16 moles of ethyelene oxide (OPE‐16), octylphenol ethoxylate with 30 moles of ethyelene oxide (OPE‐30) as non‐ionic surfactants of varying poly(ethylene oxide) hydrophilic head dimension. From the increase in fluorescence intensity of curcumin in the presence of surfactants, we had estimated the apparent binding constant (Kb) of curcumin‐micelle complex formation. The evaluated Kb values between curcumin and CTAB, TTAB, and DTAB were 7.75 × 105, 3.44 × 105, and 0.78 × 105 L mol−1, respectively. In the case of non‐ionic surfactants, the estimated Kb values of curcumin with OPE‐10, OPE‐16, and OPE‐30 were 4.90 × 106, 3.82 × 106, and 0.58 × 106 L mol−1, respectively. Thus, it was found that Kb values were somehow greater in the case of non‐ionic surfactants than cationic surfactants. From the fluorescence quenching study it was revealed that the probable location of curcumin was the Stern layer and the palisade layer in the case of cationic and non‐ionic micelles, respectively. Our results might be useful to overcome challenges associated with the delivery of curcumin as a multifunctional drug molecule.

Single-Molecule Interactions at a Surfactant-Modified H2 Surface Nanobubble.

In schematics and cartoons, the gas-liquid interface is often drawn as solid lines that aid in distinguishing the separation of the two phases. However, on the molecular level, the structure, shape, and size of the gas-liquid interface remain elusive. Furthermore, the interactions of molecules at gas-liquid interfaces must be considered in various contexts, including atmospheric chemical reactions, wettability of surfaces, and numerous other relevant phenomena. Hence, understanding the structure and interactions of molecules at the gas-liquid interface is critical for further improving technologies that operate between the two phases. Electrochemically generated surface nanobubbles provide a stable, reproducible, and high-throughput platform for the generation of a nanoscale gas-liquid boundary. We use total internal reflection fluorescence microscopy to image single-fluorophore labeling of surface nanobubbles in the presence of a surfactant. The accumulation of a surfactant on the nanobubble surface changes the interfacial properties of the gas-liquid interface. The single-molecule approach reveals that the fluorophore adsorption and residence lifetime at the interface is greatly impacted by the charge of the surfactant layer at the bubble surface. We demonstrate that the fluorescence readout is either short- or long-lived depending on the repulsive or attractive environment, respectively, between fluorophores and surfactants. Additionally, we investigated the effect of surfactant chain length and salt type and concentration on the fluorophore lifetime at the nanobubble surface.

The electrokinetic properties of cationic surfactants adsorbed on a hydrophobic substrate: effect of chain length and concentration

Electrokinetic (EK) properties, such as the electro-osmotic flow (EOF), are influenced by surfactant adsorption at the solid–liquid interface. With the growing popularity of poly(methyl methacrylate) (PMMA) as the substrate for polymeric-based microfluidics, it is important to understand the effect of surfactants on EOF in these devices. Here, we investigate the effect of surfactant chain length and concentration on the electro-osmotic (EO) mobility induced by three cationic surfactants cetyl trimethylammonium bromide (CTAB), trimethylammonium bromide (TTAB), dodecyl trimethylammonium bromide (DTAB) in PMMA microcapillaries. The EO mobility curve as a function of concentration shows three regimes. First, at very low concentrations below 0.002 mM, the mobility is constant and approximately equal to the value obtained with the surfactant-free electrolyte (1 mM KCl). Next, the EOF reverses and mobility increases linearly with surfactant concentration. Finally, the mobility reaches a plateau at a concentration well below surfactant CMC (0.2-mM CTAB, 0.5-mM TTAB and 2-mM DTAB) and decreases at the vicinity of CMC. Our results show that the rate of change in mobility with respect to concentration is a linear function of chain length and increases with longer-chain surfactants. In addition, we deduce the magnitude of Van der Waals or cohesive energy between the adsorbed alkyl chains from the EO mobility values. For the alkyl trimethylammonium surfactants adsorbed on the hydrophobic surface of PMMA, this energy was found to be 0.114 kT smaller than the reported value for ionic surfactants adsorbed on a hydrophilic surface.

The Effect of Surfactant Chain Length and Type on the Photocatalytic Activity of Mesoporous TiO2 Nanoparticles Obtained via Modified Sol-Gel Process

Mesoporous amorphous and nanocrystalline titanium dioxide were prepared by simple and environmental friendly modified Sol-Gel method using cationic (C14TAB, C16TAB, C18TAB) and nonionic (Plantacare UP K55) surfactant as pore forming agent. The obtained particles were characterized by BET, TEM, FT-IR and XRD techniques. The effect of cationic surfactant chain length and type of template on the photocatalytic activity of as prepared TiO2 nanoparticles were investigated by the degradation of rhodamine B in water solution under UV irradiation. The results indicated that this process was well described by pseudo-first order kinetic model. All the prepared titanium dioxide particles with cationic and nonionic surfactant exhibited higher performance for rhodamine B photo-degradation. The sample with large pore size and small particle size which obtained by using C18TAB surfactant showed high photocatalytic activity compared with the others samples and commercial P25. The mechanism of photocatalytic degradation of rhodamine B was proposed based on the degradation products determined by GC/MS and LC/MS. The performance of the recycled TiO2 as photocatalyst was investigated.

Metallic anion removal from dilute aqueous solutions using polymer-surfactant aggregate process: Effect of surfactant chain length

A novel process was developed to remove metallic anions from dilute aqueous solutions using polymer-surfactant aggregates (PSAs). This process uses a cationic surfactant to form micelle-like aggregates on oppositely charged polymer chains, thus forming PSAs. The PSAs can bind with dilute anions and self-flocculate. Subsequently, the anion-loaded PSA flocculates can be separated from the solution by gravity settling. The concentration of chemical residue, however, is relatively high in the treated water. To improve the quality of treated water and reduce the chemical usage, two different surfactants containing a 16-carbon chain have been investigated individually. The results show that an extended chain surfactant can decrease the concentration of chromate after treatment from 7ppm (0.06mM) to 0.5ppm (0.004mM) and the concentration of residual surfactant from 1mM to 0.02mM, using the same polymer. The PSAs formed with an extended chain surfactant work effectively at a salinity below 300mM KCl and a temperature below 50°C. These results suggest that the PSAs formed with a longer chain surfactant enhance the effectiveness of treating dilute metallic anions, and at the same time lead to much less surfactant residue in the treated water. Such a PSA process has potential application in the efficient removal of dilute metallic anions during process aqueous effluent treatment.

Wettability modification of lignite by adsorption of alkyltrimethylammonium bromides with different alkyl chain length

ABSTRACTTo overcome the problem of moisture re-adsorption of dried lignite with common evaporation drying methods, a set of linear alkyl quaternary ammonium surfactants (C10TAB, C12TAB, and C16TAB) were used to modify lignite surface, and the effects of alkyl chain length on the adsorption characteristics of surfactants and wettability of lignite surface were evaluated. Pseudo-first and pseudo-second-order kinetic models and Langmuir model were, respectively, used to simulate adsorption kinetics and adsorption isotherms. The results showed that three surfactants gradually formed double-layer adsorption on lignite surface and the loading of surfactant increased with the length of alkyl chain. X-ray photoelectron spectroscopy analysis showed that C3H9N+ moiety of the surfactants would preferentially interact with O˭C‒O groups of lignite. Results of wetting heating and moisture re-adsorption showed that three surfactants obviously decreased hydrophilicity and restrained moisture re-adsorption of lignite, but with the formation of double-layer adsorption, hydrophilic headgroups of surfactant faced outward, which caused increase in hydrophilicity of lignite. As a result of two opposite effects of surfactant chain length on lignite wettability, the effect of C12TAB on decreasing hydrophilicity was the best among the three chosen surfactants.

Effect of surfactant chain length on drug release kinetics from microemulsion-laden contact lenses

The effect of surfactant chain lengths [sodium caprylate (C8), Tween 20 (C12), Tween 80 (C18)] and the molecular weight of block copolymers [Pluronic F68 and Pluronic F 127] were studied to determine the stability of the microemulsion and its effect on release kinetics from cyclosporine-loaded microemulsion-laden hydrogel contact lenses in this work. Globule size and dilution tests (transmittance) suggested that the stability of the microemulsion increases with increase in the carbon chain lengths of surfactants and the molecular weight of pluronics. The optical transmittance of direct drug-laden contact lenses [DL-100] was low due to the precipitation of hydrophobic drugs in the lenses, while in microemulsion-laden lenses, the transmittance was improved when stability of the microemulsion was achieved. The results of in vitro release kinetics revealed that drug release was sustained to a greater extent as the stability of microemulsion was improved as well. This was evident in batch PF127-T80, which showed sustained release for 15days in comparison to batch DL-100, which showed release up to 7days. An in vivo drug release study in rabbit tear fluid showed significant increase in mean residence time (MRT) and area under curve (AUC) with PF-127-T80 lenses (stable microemulsion) in comparison to PF-68-SC lenses (unstable microemulsion) and DL-100 lenses. This study revealed the correlation between the stability of microemulsion and the release kinetics of drugs from contact lenses. Thus, it was inferred that the stable microemulsion batches sustained the release of hydrophobic drugs, such as cyclosporine from contact lenses for an extended period of time without altering critical lens properties.

The effect of surfactant chain length on the morphology of poly(methyl methacrylate) microcapsules for fragrance oil encapsulation

The solvent evaporation method for producing microcapsules relies upon the correct wetting conditions between the three phases involved in the synthesis to allow core-shell morphologies to form. By measuring the interfacial tensions between the oil, polymer and aqueous phases, spreading coefficients can be calculated, allowing the capsule morphology to be predicted. In this work we explore the effect of surfactant chain length on capsule morphology using poly(methyl methacrylate) as the polymer and hexadecane as the core. We compared the predicted morphologies obtained using the polymer as a solid, and the polymer dissolved in dichloromethane to represent the point at which capsule formation begins. We found that using the polymer in its final, solid form gave predictions which were more consistent with our observations. The method was applied to successfully predict the capsule morphologies obtained when commercial fragrance oils were encapsulated.

Interfacial effects and emulsion stabilization by in situ surfactant generation through the saponification of esters

The stabilization of oil-in-water emulsions is critical for a wide variety of fields. Here, we explore the reaction dynamics of and emulsion stabilization by in situ surfactant generation through the saponification of esters that are commonly used in cosmetics and drug delivery. We combine measurements of dynamic interfacial tension and surface elasticity with emulsion stability to determine the dynamics of the interfacial reaction and its effect on interfacial properties. The rate of surfactant production through the in situ reaction depends on the surface area and thus the dynamics measured in a pendant drop may not reflect the dynamics in emulsification. To test this, we also measure the dynamics of surfactant production after emulsification. Further, we explore the effect of surfactant chain length and solution pH on the interfacial tension dynamics and the emulsion stability. The results show that the interfacial tension transients in a pendant drop correlate with the in situ reaction dynamics but that there are others factors to consider. The steady state interfacial tension represents a pseudo-steady state between rate of surfactant produced and that desorbing into the aqueous phase. The interfacial tension dynamics and emulsion stability also depend strongly on the charge. The emulsions retain stability after aqueous pH neutralization, suggesting that a portion of the adsorbed surfactant molecules remain ionized at neutral pH. Emulsion stability increases with increasing surfactant chain length, which is the expected trend because a longer chain length reduces aqueous solubility thereby increasing the surfactant surface coverage. Therefore, the approach of emulsion stabilization by in situ surfactant production is more useful for surfactants with very low aqueous solubility. Finally, the transients of surfactant concentration in the emulsions show a reduction in the rate of the in situ reaction with increasing coverage of the surface by the adsorbed anionic surfactant most likely due to the buildup of surface charge that reduces the concentration of the hydroxyl ions at the surface.

Mixed reverse micellar extraction and effect of surfactant chain length on extraction efficiency

Abstract This study investigated the effect of surfactant chain length on mixed reverse micellar extraction of cellulase. The mixed reverse micelle systems were formed by biosurfactant rhamnolipid and a nonionic surfactant tween (tween-20, tween-40, tween-60, or tween-80). Electron spin resonance (ESR) method was used in order to find the suitable chain length of tween and the best ratio of rhamnolipid/tween mixture. The key parameters such as pH and temperature in forward and backward extraction were studied, and the results showed that mixed reverse micelle with different surfactant chain length had different pH sensitivities. Rhamnolipid/tween-80 system was more sensitive to pH than other systems, and rhamnolipid/tween-20 system was the least sensitive to pH among four systems. The experimental results also showed that chain length had limited sensitivity to temperature. Rotation correlation time of cellulase solutions (original and extraction) were investigated, which proved the superiority of longer chain length system (rhamnolipid/tween-80 system).

Molecular mechanism of micellar catalysis of cross aldol reaction: Effect of surfactant chain length and surfactant concentration

The importance of alkyl chain length and concentration of quaternary ammonium surfactants (QAS) in the micellar catalysis of cross aldol reaction was investigated. The NaOH-micellar system catalyzed aldol reaction of benzaldehyde and cyclohexanone to α,α′-dibenzylidene cyclohexanone (di condensation/desired product) over mono condensation product was used as model reaction for this study. The C16QAS micellar system (QAS with n-hexadecyl group) gave highest cyclohexanone conversion (90%) to desired product (82%) showing that C16QAS micellar system possesses optimum properties and/or microenvironment for this reaction. Furthermore, the micellar system with high surfactant concentration (C16QAS; >150mM) made the reaction faster giving >99% conversion to selectively desired product (>99%) within 30min The large interface created by C16QAS micelles in the aqueous medium at high surfactant concentration makes the reaction faster by facilitating the interaction of hydrophobic reactants and water soluble catalyst (OH− ions). The activation of benzaldehyde molecules, their localization preferably near the interface and stabilization of enolate ions (reactive intermediates) by micellar system at high surfactant concentration were observed to be promoting the cross reaction selectively to the desired product.

Novel Viscoelastic Systems from Azobenzene Dye and Cationic Surfactant Binary Mixtures: Effect of Surfactant Chain Length

Sodium 4-[(E)-phenyldiazenyl] benzoate (AZONa), a photo-responsive dye, induced micellar growth in alkyl-trimethylammonium bromide (dodecyl-, DTAB; tetradecyl-, TTAB; cetyl-, CTAB and octadecyl-, OTAB) solutions was investigated using light scattering and viscosity. The viscosity decrease upon increasing [surfactant] to above about 20 mM was found to be common from TTAB to OTAB solutions at fixed mole ratio of [AZONa]/[surfactant]. Cryo-TEM demonstrated that the decrease of viscosity was attributed to the entangled linear to multi-connected saturated network wormlike micelles transition. UV-vis spectra showed that AZONa interacted strongly with OTAB as revealed from both the shifting of absorbance peak and the variation of absorbance intensity, which suggest the binding of AZONa to OTAB micelles. 1H NMR confirmed the solubilization of AZONa to the palisade layer and growth of micelles upon increasing [AZONa] as revealed from the shifting and broadening of peaks.

Effect of Surfactant Chain Length on the Rheological Properties of Cationic Surfactants and a Hydrophobic Counterion

The rheological behavior of alkyimethylammonium 2-hydroxy-1-carboxy-naphthoate, CxTA-2.1-HCN (x = 16, 14, 12, 10, and 8) is presented. With increasing 2.1 HNC/CxTAOH (x = 16, 14, 12) ratio, the viscoelasticity of the solutions changes due to a transition in the micellar shape from small micelles to rodlike micelles and finally to multilamellar vesicles (MLV). On the other hand, a transition from small micelles to multilamellar vesicles (MLV) was observed for solution with CxTA-2.1-HCN (x = 10 and 8). The MLV phases behave like a weak gel and have a yield stress value. Rheological measurements were performed for these viscoelastic systems in order to find out the dependency of the viscoelastic behavior on the surfactant chain length and hydrophobic counterion concentration. Some theoretical models as reptation mechanism was also applied in order to get some structural details and to illustrate the rheological behavior of these viscoelastic systems. Some models that correlate MLV-modulus on the surfactant morphology are also presented and discussed.

Mixed Polyelectrolyte−Surfactant Langmuir Monolayers at the Air/Water Interface

Polystyrenesulfonate acid (PSS) and alkyltrimethylammonium bromide (CnTAB, n = 8, 14, or 18) were dissolved in a chloroform/methanol solution and cospread on an air/water interface. The surfactant−polyelectrolyte interaction leads to the formation of hydrophobic complexes which are able to spread well at the air/water interface. The effects of surfactant chain length and surfactant/polymer ratio on the characteristics of the mixed monolayers were studied in terms of surface pressure−area (π−A) isotherm, area relaxation, and hysteresis behavior as well as the surface morphology and composition of the corresponding Langmuir−Blodgett films. The mixed monolayers prepared by cospreading method are also compared with the complex monolayers prepared by preprecipitation of the surfactant−polyelectrolyte complexes from an aqueous solution. The experimental results show that the chain length of an incorporated surfactant is the main factor determining the properties of a complex monolayer. By using a longer chain surfactant to complex with polyelectrolyte, a more condensed monolayer with higher collapse pressure and stability can be obtained. For the effect of surfactant/polymer ratio (S/P), it is found that an increase of S/P ratio not only produces more complexes capable of staying at the air/water interface but also affects the incorporation of uncomplexed surfactant into the mixed monolayer. The X-ray photoelectron spectroscopy (XPS) analysis shows that the amount of uncomplexed surfactant is higher at low S/P value (0.2) and is insignificant when the S/P value increases to about 1.0 or 2.0, where a maximum amount of complexes were formed at the interface. A further increase of S/P ratio may cause additional incorporation of uncomplexed surfactant and/or micellization of surfactant around PSS cores, depending on the surfactant chain length. A model illustrating the incorporation and spreading of the surfactant−polyelectrolyte complexes at the air/water interface was proposed.

Effect of Surfactant Chain Length on the Binding Interaction of a Biological Photosensitizer with Cationic Micelles

Steady-state and time-resolved fluorometric techniques have been exploited to study the photophysical and distribution behavior of an efficient cancer cell photosensitizer, norharmane (NHM), in well-characterized, biomimicking nanocavities formed by cationic micelles with varying surfactant chain length. Amphiphiles like dodecyl trimethyl ammonium bromide (DTAB), tetradecyl trimethyl ammonium bromide (TTAB), and cetyl trimethyl ammonium bromide (CTAB) have been used for the purpose. Emission behavior of NHM is very much dependent on the surfactant concentration as well as their hydrophobic chain length. The binding constant (K) and free-energy change (DeltaG) for the interaction of NHM with the cationic micelles have been determined from the fluorescence data. Polarity of the microenvironment around the probe has been determined in the cationic micellar environments from a comparison of the variation of fluorescence properties of the two-prototropic species of the probe in water/dioxane mixture with varying composition. Experimental results demonstrate that the variation in the cationic surfactant chain length plays an important role in promoting a specific prototropic form of the probe molecule. Fluorescence decays are biexponential in all the micelles indicating that the probe molecules are distributed between the two distinct regions of the micelles. The population of the component with a longer lifetime corresponds to the probe in the head group site, while the short-lived component comes from the probe bound to the core region of the micelles. On the basis of the lifetime measurements, the partitioning behavior of the chromophore in the head group and in the core regions in the micelles has been determined.

Effect of Surfactant and Solvent Properties on the Stacking Behavior of Non-aqueous Suspensions of Organically Modified Clays

Montmorillonite clay was treated with quaternary ammonium surfactants with 1-3 long chains of 10-18 carbons to form organoclays which can be suspended in non-aqueous solvents. The effects of surfactant chain length, number of long chains, and the properties of the solvent on the colloidal behavior of the surfactant coated clay plates were studied using small-angle X-ray scattering. The scattering data were modeled using a one-dimensional aggregation theory to describe the stacking of the clay plates. The plates self-organize into stacks with a reproducible basal spacing in the range of 30-50 A, and for each surfactant, the basal spacing falls into one of two preferred distances. We interpret this by considering that the surfactant layer on the clay has two strata, one being the polar near-clay headgroup region and the other the nonpolar alkane chain region. Polar solvents will swell the polar stratum preferentially while nonpolar solvents will swell the nonpolar stratum of the surfactant. As the nonpolar stratum is larger than the polar one, the nonpolar solvents increase the basal spacing between the clay plates more than the polar solvents. The number of long chains on the surfactant does not have an effect on the basal spacing, as the density of surfactant molecules on the surface is low enough to allow the unimpeded swelling of the chains. The one-dimensional aggregation theory can be used to determine the number of plates in a stack, but the effect of changing clay particle size or concentration is not as great as would be expected from this theory. This may be due to the formation of large-scale structures in the suspensions which prevent a true equilibrium stack size being attained.

Phase Behavior of Polyion−Surfactant Ion Complex Salts: Effects of Surfactant Chain Length and Polyion Length

The aqueous phase behavior of a series of complex salts, containing cationic surfactants with polymeric counterions, has been investigated by visual inspection and small-angle X-ray scattering (SAXS). The salts were alkyltrimethylammonium polyacrylates, CxTAPAy, based on all combinations of five surfactant chain lengths (C6, C8, C10, C12, and C16) and two lengths of the polyacrylate chain (30 and 6 000 repeating units). At low water contents, all complex salts except C6TAPA6000 formed hexagonal and/or cubic Pm3n phases, with the hexagonal phase being favored by lower water contents. The aggregate dimensions in the liquid crystalline phases changed with the surfactant chain length. The determined micellar aggregation numbers of the cubic phases indicated that the micelles were only slightly aspherical. At high water contents, the C6TAPAy salts were miscible with water, whereas the other complex salts featured wide miscibility gaps with a concentrated phase in equilibrium with a (sometimes very) dilute aqueous solution. Thus, the attraction between oppositely charged surfactant aggregates and polyions decreases with decreasing surfactant chain length, and with decreasing polyion length, resulting in an increased miscibility with water. The complex salt with the longest surfactant chains and polyions gave the widest miscibility gap, with a concentrated hexagonal phase in equilibrium with almost pure water. A decrease in the attraction led to cubic-micellar and micellar-micellar coexistence in the miscibility gap and to an increasing concentration of the complex salt in the dilute phase. For each polyion length, the mixtures for the various surfactant chain lengths were found to conform to a global phase diagram, where the surfactant chain length played the role of an interaction parameter.

Adsorption of Oppositely Charged Polyelectrolyte/Surfactant Mixtures. Neutron Reflection from Alkyl Trimethylammonium Bromides and Sodium Poly(styrenesulfonate) at the Air/Water Interface: The Effect of Surfactant Chain Length

The interactions between a series of cationic surfactants (alkyltrimethylammonium bromides) (CnTAB) and the anionic polymer sodium poly(styrenesulfonate) (NaPSS) have been studied using surface tension and neutron reflectivity. The effect of surfactant chain length on surfactant/polymer adsorption has been studied using chain lengths from 10 to 16 carbon atoms (i.e. C10TAB to C16TAB). The surface tension plots (γ against ln c) have two types of shape. The C10TAB and C12TAB with NaPSS systems have plots with plateaus, while the longer chain C 14TAB and C16TAB systems have a pronounced hump in the surface tension at surfactant concentrations just below the critical micelle concentration (cmc) of the free surfactant. Neutron reflection shows that there is a surfactant monolayer (thickness 20−22 A) adsorbed at dilute surfactant concentrations for the C10TAB, C12TAB, and C14TAB systems, but this changes to a thick layer (60−100 A) at concentrations closer to the cmc. The corresponding areas per adsorbed surfac...

Ferrocene Groups Tethered to Clay Surfaces : Effect of Surfactant Chain Length on Electroactivity

A homologous series of ferrocenyl surfactants, where 6, or 11, have been intercalated into thin clay films in an effort to design novel electroactive nanocomposites. Cyclic voltammetry of clay-modified electrodes has been used to investigate the electrochemical properties of the surfactants. The rate of intercalation into the clay and steady-state currents were found to be highly dependent on chain length. Of the three, the compound containing one carbon in the chain is the only molecule to be effectively modeled by an ion-exchange mechanism, implying that the ferrocene resides close to the surface of the clay. The electrochemistry of the two longer chain compounds is markedly different from the one with a single carbon in the chain. The six- and eleven-carbon chain compounds have been shown to generate a larger capacitive current in the clay and represent possible charge-storage devices. © 2002 The Electrochemical Society. All rights reserved.